2007-10-02

CHICAGO, Oct. 2 -- A neat orderly mind augmented by a conscientious personality tends to resist Alzheimer's disease, researchers here found.

Self-disciplined and goal-directed persons who scored high on a standard measure of conscientiousness had an 89% lower risk of developing Alzheimer's than those with low scores, Robert S. Wilson, Ph.D., of Rush University, and colleagues, reported in the October issue of the Archives of General Psychiatry.

Conscientiousness was associated with mild cognitive impairment and Alzheimer's, but not with the pathologic hallmarks of these conditions such as neurofibrillary changes, they said.

Epidemiologic research has shown that conscientiousness is associated with a wide range of mental and physical disorders, disability, and death, suggesting that the trait has some general role in health maintenance, the researchers said.

In addition, a number of variables associated with Alzheimer's risk, including educational and occupational attainment, physical exercise, tobacco use, and depressive symptoms, are also associated with conscientiousness, suggesting that the trait may have a more specific link to the development of Alzheimer's, the researchers said.

To test this hypothesis, Dr. Wilson and colleagues studied 997 older Catholic nuns, priests, and brothers without dementia at enrollment in 1994, recruited from more that 40 groups across the U.S.

Participants had standard evaluations that included medical history, neurology examinations, and cognitive testing.

They also completed a standard 12-item measure of conscientiousness. The participants rated agreement on a scale of one to five with items, such as "I am a productive person who always gets the job done."

Conscientiousness scores ranged from 11 to 47, with a higher score indicating a greater degree of conscientiousness. The mean conscientiousness score was 34 out of 48.

Conscientiousness was higher in women than in men and was not related to age or education.

During up to 12 years of annual follow-up by 2006, 176 participants developed Alzheimer's disease.

In a proportional hazards regression model adjusted for age, sex, and education, a high conscientiousness score in the 90th percentile (40 points) was associated with about an 89% reduction in risk of Alzheimer disease compared with a low score of 28 points (the 10th percentile), the investigators found.

Results were not substantially changed by controlling for other personality traits, activity patterns, vascular conditions, or other risk factors.

Because mild cognitive impairment is increasingly viewed as a state that precedes clinically evident dementia in Alzheimer's, the researchers conducted a further analysis. They found that a higher level of conscientiousness was associated with a reduced risk of mild cognitive impairment (HR, 0.977, 95% CI, 0.956-0.999).

This association remained in subsequent analyses that controlled for physical, cognitive, and social activity or for cardiovascular health, but was no longer significant in analyses that controlled for other personality traits, depressive symptoms, or the ε4 allele.

The researchers also analyzed results from brain autopsies of 324 participants who died during the study. Conscientiousness was unrelated to neuropathologic measures including brain plaques and tangles.

However, conscientiousness did appear to modify the association of neurofibrillary pathologic changes and cerebral infarction with an individual's cognitive abilities before death.

That conscientiousness is associated with a risk of dementia but not with its traditional pathologic features suggests that it may be related to some other neurodeteriorative changes that do not currently leave recognized footprints, the researchers suggested.

There are several ways conscientiousness might protect against Alzheimer's disease, the researchers said. Controlling for cardiovascular health and lifestyle activity patterns did not substantially affect the findings, they found.

It is possible, they said, that conscientious individuals may be likelier to experience educational and occupational success, both of which have been associated with a reduced risk of Alzheimer's disease.

Conscientiousness is also associated with a higher level of resilience and greater reliance on task-oriented coping.

These factors, they said, might decrease the adverse effect of negative life events and chronic psychological distress associated with a risk of dementia in older age.

The main limitation of the study, the researches said, is that the data were based on a selected group of people who differ from the general population in education and lifestyle so that studying more representative cohorts is important.

Also, they noted that conscientiousness is a somewhat heterogeneous trait complex, but the brief measure used in this study precluded investigation of its subcomponents.

Understanding the mechanisms linking conscientiousness to maintaining cognition in older age may suggest novel strategies for delaying the symptoms of Alzheimer's disease, Dr. Wilson and colleagues wrote.

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